Modifications to the theory of intraglacial waterways for the case of subglacial ones

ABSTRACT. It is argued that in temperate mountain glaciers, waterways are subglacia l. It is shown that the theory of Spring and Hutter (i 981) for intrag lacial flooded conduits leads to an equation for the g rade line which differs from Riithli sberger's (i 972) only by negligible terms, and a slight modification of the ex ponent of the di scharge. For a subglacial flooded waterway two important processes should in stead be introduced: the enh ancement of plastic deformation on the up-stream side of bumps, and the heat afforded by g ro und water (which in winter accounts for most of the di scharge). The theory modified in thi s way explain s wh y Riithli sberger had to adopt an unreali stic value for the rheological para meter of ice. It lead s to the conclusion that in areas wh ich a re not overdeepened, most of the year subglacial waterways should remain not flooded and a t atmospheric pressure. The case o f overdeepening is examined. Fina ll y the implication s of thi s new model for g lacier sli ding theory are demonstrated. RESUME. Modifications a /a theorie des torrents intra-g/ociaires dans /e cas oli ifs sont sous-g /aciaires. On defend ridee que, dans les glaciers de montagne temperes, les voies d'eau sont sous-glaciaires. On montre que la theorie de Spring et Huller ( 1981) po ur des conduits noyes intra-glaciai res conduit it une equation pour la ligne piezometrique qui ne differe de celle de Rothlisberger ( 1972) que par des termes negligeables, et une lege re modification de I'exposant du debit. Po ur un conduit noye sous-glac iaire il faut plutot introduire deux processu